Method of bonding copper to aluminum or aluminum alloys



Patented Dec. 15 1953 METHOD OF BONDING COPPERz-TO-ALUx- OR ALUMIN ALLOYS CaflR. Gul'verhouse, Jr., Birmingham, Ala assignor to Anderson Brass Works, acorporation of Alabama No Drawing. Application J my 19,. 195.0,; Serial N0. 174,796

10 Claims;

Thisinvention relates to avchemically coated aluminum article and the method of. producing the. same,. and has. for its.principal object the proyisionoi such-a methodwhereby a=suitable metallis chemically. deposited on the aluminum from an. alkali bath andisthenchem-ically replaced by. another-metal-from an acid bathcontaining complex ions, said replacing metal beingbelow the-metal.replacedin the. activity series oi; metals thus, obtaining, as a result an aluminum articlerhaving directly, strongly adherently bonded to its surface a. coating of the desired metal.

Another obj ect of myinvention; is to provide a method;- f coating, aluminum with copper whereby. zinc is first. chemically; deposited on the aluminum from an alkali: bath. and is. then replaced by-copper by chemical reactionv from: an acid bathof copper fiuoborate.

A- further object" is. to provide. a method of coating articles. of both pure aluminum and aluminum alloys whereby a strongly adherent andreyengooating 1S5 deposited on the same and in;whioh:the'adhera'bility of the coating is-substantially unalfected by. theparticular; kind Y. of aluminum; alloy tobecoated;

A .furtherobject: isto provide a method :of 6188-. trjoplatingl aluminum; whereby it: is.- unnecessary tmfirst: provide cyanide. strike or: coating before electroplating,- resulting ima, direct: bond; between thez-base metal: and the; coating.

Briefly, my invention comprises degreasing and chemically cleaningthe article-of aluminum or aluminum alloy to be coated. The article thus cleanedis immersed iha sodium or potassium zincate solution where an even-coating of zinc is obtained thereon. The zinc coated article is rinsedf inwater and then immersed in an acid solution orj co' per fiuobor'ate where the zinc goes into solution and is chemicany' replaced on. the surface of the article by the copper from the copper fluoborate solution.

Heretofore, so far' as I am aware, coatingsof dopper have been deposited on pure aluminum and special processes have been devised to coat particular-aluminum alloys, but there has beenno. satisfactory methodof coating pure aluminum; and all aluminum alloys with copper by any one process. I have. found that by first coating aluminum or aluminum alloys with zinc and then chemically replacing the zinc with copper an even and strongly adherent coat of copper is obtained. I have thus provided a process equally adaptable to coating aluminum or aluminum alloys which is not dependent upon the proximately 30 seconds and. then' rinsing; the

article. in water. Next; the article is' immersed in 20% caustic soda, for approximately 15 sec ondsthereby giving alight causticetch" to the surface of thealuminum and then rinsedin Wazter. The. time of, caustic etching may: vary with the alloy ofaluminum to .be coated; In any'case; only a lightcaustic etchis necessary. Theal'uiminum articleis then-immersed for 1'5 seconds in a solution consisting off 3) parts concentrated nitric acid and.1 part.48%l hydrofluoi'i'cacidi and againrinsed in water.

The aluminum article thus chemically cleaned is coated Witha uniform coating ofzinc byimmersing it for approximately 2 minutes. in a 15.01111- tion of. sodium zincate or potassium .ziinc'ate having a pH at such avalue that the aluminum will not be burned... I have found, in actuali practi'ce that a, pH of approximately. lojis ,sati'sfactory for most aluminum alloys. 'Ijhezincate solution may consist of approximately 100, grams per literof zinc oxide and approximately 525. grams per liter of sodium hydroxide, While the, zinc coating produced on the aluminum by. this immersionis evenand strongly. adherent, an. outer. spongy coating of zinc is ,formed over, the, adherentv coat ing of, zinc which may be removedlby. rinsing, the article in water.

After removing the outer. spongy. portion, of the zinc coating, it isimmersedgin an, acid solution' which may consist of. approximately 448 grams per. liter. of copperfluoborate (375210.319? Baum). The temperature. ofthe copper fluoborate solution. is'maintai'ned at from 810101170. F. while the zinc coatedaluminum is. immersed therein. Any-suitable vessel,.such as onemade from methyl methacrylate may be used for the acid bath. The zinc coating on the aluminum is chemically replaced by the copper from the copper fluoborate solution, the zinc ions going into solution. A very thin and uniform coating of copper is thus obtained on the aluminum. A complete coating of the copper for the aluminum is assured since the chemical reaction continues 'until the zinc is completely replaced by the copper. This thin coating of copper may be built up by methods of electroplating on copper which are well known in the art to which my invention relates. It will be apparent that metals other than copper may be electroplated on said copper coating.

From the foregoing it will be apparent that I have devised an improved method of coating aluminum and its alloys. I provide an even and strongly adherent coating of copper on the aluminum by chemically replacing a chemically deposited coating of zinc with the copper, and hence the coating does not blister or become separated from the surface of the aluminum. For use in those cases where pure aluminum and aluminum alloy articles are to be plated, my invention makes unnecessary the provision of separate vats and equipment, hence reducing equipment costs in the plating plant.

While I have described my invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof, and I, desire, therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims.

What I claim is:

1. The method of firmly bonding a coating of copper directly to an aluminum article comprising degreasing the surface of the article, cleaning the surface of the article by immersing the same in a concentrated nitric acid solution and subsequently rinsing the article with water, immersing the article in an aqueous caustic soda solution and subsequently rinsing with water, immersing the article in an aqueous solution consisting of concentrated nitric acid and hydrofiuoric acid and subsequently rinsing with water, depositing zinc on the article by immersing it in an aqueous solution of an alkali zincate having a controlled pH of approximately 10, rinsing the zinc-coated article with water, and chemically replacing the zinc with copper by immersing the zinc-coated article in an aqueous acid solution of copper fiuoborate.

2. The method of firmly bonding a coating of copper directly to an aluminum article comprising degreasing the surface of the article, cleaning the surface of the article by immersing the same in a concentrated nitric acid solution for approximately 30 seconds and rinsing the article with water, immersing the aluminum article for approximately 15 seconds in an aqueous caustic soda solution and subsequently rinsing with water, immersing the article in an aqueous solution consisting of approximately 3 parts concentrated nitric acid and 1 part 48% hydrofluoric acid and subsequently rinsing with water, depositing zinc on the article by immersing it for approximately two minutes in an aqueous solution of sodium zincate having a controlled pH of approximately 10, rinsing the zinc-coated article with water, and chemically replacing the zinc with copper by immersing the zinc-coated article in an aqueous acid solution of copper fiuoborate at a temperature of from 80 to 170 F.

3. The method of firmly bonding a coating of copper directly to an aluminum article as defined in claim 2 in which the zincate solution consists of appoximately 100 grams per liter of zinc oxide and approximately 525 grams per liter of sodium hydroxide.

4. The method of firmly bonding a coating of copper directly to an aluminum article as defined in claim 2 in which the copper fiuoborate solution consists of approximately 448 grams per liter of copper fiuoborate at 37.5 to 39 Baum.

5. The method of firmly bonding a coating of copper directly to an aluminum article as defined in claim 2 in which the article is degreased in trichloroethylene vapors.

6. The method of firmly bonding a coating of copper directly to an aluminum article as defined in claim 2 in which the article is degreased by immersion in a solution of carbon tetrachloride.

7. The method of firmly bonding a coating of copper directly to an aluminum article as defined in claim 2 in which the article is degreased with a detergent.

8. The method of firmly bonding a coating of copper directly to aluminum or aluminum alloys comprising degreasing and cleaning the surface of the aluminum to be coated, immersing the aluminum thus degreased and cleaned in an aqueous solution of potassium zincate, thereby depositing zinc on the aluminum, and chemically replacing the zinc with copper by immersing the zinc-coated aluminum in an aqueous acid solution of copper fluoborate.

9. The method of firmly bonding a coating of copper directly to aluminum or aluminum alloys comprising degreasing and cleaning the aluminum to be coated, immersing the aluminum thus degreased and cleaned in an aqueous solution of sodium zincate thereby depositing zinc on the aluminum, and chemically replacing the zinc with copper by immersing the zinc-coated aluminum in an aqueous acid solution of copper fiuoborate.

10. The method of firmly bonding a coating of copper directly to aluminum or aluminum alloys comprising degreasing and cleaning the aluminum to be coated, immersing the aluminum thus degreased and cleaned in an aqueous solution of an alkali zincate, thereby depositing zinc on the aluminum, and chemically replacing the zinc with copper by immersing the zinc-coated aluminum in an aqueous acid solution of copper fiuoborate.

CARL R. CULVERHOUSE, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 723,717 Nicholson Mar. 24, 1903 1,405,534 Merritt Feb. 7, 1922 1,457,149 Cunningham May 29, 1923 1,627,900 Hewitson May 10, 1927 2,398,738 Gilbert Apr. 16, 1946 2,403,426 Doutz et al. July 2, 1946 2,580,773 Heiman Jan. 1, 1952 OTHER REFERENCES Struyk et al., Copper Plating from Fluoborate Solutions, Amer. Electroplaters Soc. vol. 33, September 1946, pages 923-934. 

10. THE METHOD OF FIRMLY BONDING A COTTAGE OF COPPER DIRECTLY TO ALUMINUM OR ALUMINUM ALLOYS COMPRISING DEGREASING AND CLEANING THE ALUMINUM TO BE COATED, IMMERSING THE ALUMNIUM THUS DEGREASED AND CLEANED IN AN AQUEOUS SOLUTION OF AN ALKALI ZINCATE, THEREBY DEPOSITING ZINC ON THE ALUMINUM, AND CHEMICALLY REPLACING THE ZINC WITH COPPER BY IMMERSING THE ZINC-COATED ALUMINUM IN AN AQUEOUS SAID SOLUTION OF COPPER FLUOBORATE. 